By way of background, the dental profession has been involved to an increasing degree with the well known osseointegrated implant system to facilitate dental prosthesis.
In order to properly install an implant, a tomographic x-ray of the proposed site should be taken so that the dentist can investigate the adequacy of the osseous tissue to support an implant post at the site of interest. The x-ray of the mandible or maxilla should employ tomography in order to project the cross-sectional area of the mandible or maxilla at the site of interest.
X-ray tomography, as is well known, involves rotating an x-ray source and a photographic plate in an arc relative to a patient during exposure of the x-ray image. Specifically, the x-ray source and the photographic plate are rotated through an arc about a central axis that is perpendicular to the x-ray beam. The vertical plane through the central axis is hereinafter referred to as the "tomographic plane." The result of such movement is that all bone structure in front of and behind the tomographic plane (i.e. on the sides toward and away from the plane of interest) are blurred and essentially do not appear in the image. Only the structure located at the tomographic plane appears in the x-ray image so that the image is of a cross section of the bone tissue. Therefore, by positioning the pivot point of the tomographic apparatus in a way such that the cross-sectional area that includes a particular site of interest of the mandible or maxilla of a patient will coincide with the tomographic plane, it is possible to obtain an x-ray image of the particular site of interest.
Clearly, an important consideration in the use of x-ray tomography is the accurate positioning of the anatomy of interest in the tomographic plane.
U.S. Pat. No. 4,974,423 entitled "Positioning System for X-Ray Tomography" and U.S. Pat. No. 5,431,162 entitled "Positioning Method and Apparatus for X-Ray Tomography", both commonly owned by this assignee of this application, disclose methods and apparatus for such accurate positioning of the head of a patient in relation to a tomographic apparatus which work effectively in many situations.